Change in the site density and surface acidity of clay minerals by acid or alkali spills and its effect on pH buffering capacity

Abstract

Changes in the site density and surface acidity constants (i.e. pKa 1 and pKa 2 ) of kaolinite and montmorillonite were determined after acid or alkali spills, and pH buffering capacity was evaluated as a parameter of soil function change. Surface complexation modeling with potentiometric titrations and Fourier-transform infrared spectroscopy showed that acid or alkali spills did not significantly change the surface properties of kaolinite. In montmorillonite, however, acid spills decreased the basal site density from 832 to 737 mmol kg −1 by dissolving substituted octahedral cations and decreased pKa 2 from 7.32 to 5.42 by dissolving SiOH. In response to alkali spills, the basal site density increased to 925 mmol kg −1 , and the edge site density increased from 84.8 to 253 mmol kg −1 due to AlOH and SiOH formation; thus, pKa 2 decreased to 6.78. The pH buffering capacity of acid- or alkali-spilled kaolinite at pH 6 did not significantly change, while that of acid- or alkali-spilled montmorillonite increased from 30.3 to 35.9 and 56.0 mmol kg −1 , respectively. Our results indicate that these spills greatly altered the surface properties of montmorillonite, but unexpectedly, increased the pH buffering capacity of montmorillonite.

Trace Elemental Partitioning on Clays Derived From Hydrothermal Muds of the El Tatio Geyser Field, Chile

“…The overall surface functional group density of sample 4 is relatively low when compared to the other four samples. These data correspond to a previous study that showed that acidic treatment on clay minerals can decrease pK a values and surface functional group density (Jeon & Nam, 2019).…”

“…acidic solutions (pH ∼ 0-4), as well as decreased cadmium (Cd) adsorption. Similarly, Jeon and Nam (2019) showed that acidic treatment can decrease the surface functional group density and the proton binding constants of montmorillonite. Other variations in aqueous conditions, such as pH and ionic strength, can also impact the speciation of trace elements and the surface charge of clays, and thus control the affinity of trace elements to clays.…”

Machine-learning-accelerated multimodal characterization and multiobjective design optimization of natural porous materials

“…17 Such modification of natural nanoclays may drastically change the morphology and surface activity, and in some cases it may also lead to loss of crystallity. 14,25,26 Fig. 1B further illustrates this tunability by highlighting ranges of property values achieved for various raw clay minerals with such treatments.…”

Soil vulnerability to acid or alkali spills: Identifying changes in physicochemical properties and pH buffering capacity in response to spills

“…[4][5][6] When strong acid is introduced to the soil, aluminum or iron oxide is dissolved and surface properties of clay minerals are changed. 7 Also, the dissolved Al 3+ or Fe 2+ insolubilizes phosphorus used as a nutrient to the plants, and Al 3+ replaces the exchangeable cations also used as a nutrient. [8][9][10] On the other hand, when a strong alkali is introduced into the soil, the increase in the cation concentration increases the salinity, the electrical conductivity and the concentration of toxic ions (B 3+ , Na + , Cl − , Li + ) in the soil water.…”